Light olefins have increased in value dramatically in recent years for the reason that they are building blocks for many end products, such as polyethylene and polypropylene. Past production of polypropylene was obtained by steam cracking light naphtha. The main products produced by steam cracking are ethylene and gasoline with propylene and other light olefins obtained as by products. Propylene production from steam crackers depends upon the operating rates of the steam cracker and the type of feed stock supplied. Past steam cracking technology produced propylene from heavy liquid cracking. However, most modern steam crackers use ethane-based feed leading to less propylene being produced. As such, steam cracking alone cannot satisfy the demand for propylene and there is a need of new technology to produce additional propylene to bridge the gap between supply and demand. Attempts to reconfigure the steam cracker found that there was not the flexibility of operation and also there was high energy consumption, both of which were economically unacceptable.
Attempts to reconfigure FCC units to maximize the production of propylene and light olefins created energy savings and flexibility of operations. The use of catalysts in the FCC process is found to lower the temperature for catalytic naphtha cracking, thus resulting in less energy consumption. It has been found that the addition of catalysts to improve selectivity of propylene greatly enhances the yield of propylene and other olefins. It has further been found that coke formed during the cracking process is removed by the catalyst. The catalyst is in turn decoked through catalyst regeneration. It has also been discovered that the FCC is one of the most flexible processes in refining. An FCC unit can be readily adjusted to changes in feed quality through modifications of catalyst and operating conditions.
Zeolite-based heterogeneous catalysts are commonly used in the allocation of aromatic hydrocarbons. A good example of a zeolite-based catalyst is zeolite ZSM-5.
It is an object of the invention to provide a process wherein normal hydro treated FCC gas oil feed stock is processed by a normal FCC to provide high yields of olefinic gasoline.
Shape selective catalyst additives (ZSM-5) uses the olefinic gasoline to generate olefinic LPG rating resulting in an increase in propylene yield by a factor of 2 to 3. However, ZSM-5 does not effect the same increases in butylene.
It is an object of the invention to provide a process to generate more butylene selective yields, while maintaining propylene yields.